These investigations are devoted to the development of non-invasive methods of assessing tissue structure and function. Two techniques are being developed: nuclear magnetic resonance (NMR) and optical spectroscopy/imaging. Over the last year we have made the following developments in NMR technology:1) Using the effects of deoxyhemo-globin on the magnetic relaxation properties of water, the tissue oxygen tension within the canine heart has been determined with mm resolution during adenosine or vascular occlusion. This could provide a powerful new tool in the diagnosis and guidance of treatment in heart disease. 2) A 4 Tesla 1 meter bore NMR spectro-meter has been installed and is now operational. This system has been heavily modified by the LCE staff to obtain state- of-the-art data from this device using a specially designed research console. 3) Using this device we have developed the software and hardware required to perform high resolution NMR spectroscopy and imaging experiments in man. For example a 200 micron in-plane resolution image was collected in 3 min of the human knee. 4) 31P and 13C NMR spectra of human muscle, as well as the first 14N spectrum from human muscle, have been obtained. Clinical studies concerning the handling of muscle glycogen in muscle have been initiated. 5) The magnetic susceptibility of the human chest (i.e. heart) and head has been determined and software developed to make appropriate corrections for these potential artifacts. 6) Further characterization of the proton magnetic interactions between water and macromolecules has been performed, including the temperature and magnetic field dependence of this process. Evaluation of this phenomenon with regard to detection and staging of cardiac hypertrophy and arthritis has also been performed.